Naphthoquinone cycloadduct

Brimble and McEwan (206) investigated the Diels-Alder reaction between naphthoquinones and cyclopentadiene using these catalysts. Acetylnaphthoqui-none reacts with cyclopentadiene in the presence of 67 Cu(OTf)2 to provide the cycloadduct in low selectivity (30% ee). Catalysts 269c and 269d afford lower selectivities. Improved selectivities are observed using 5-hydroxynaphthoquinone [50% ee with 67 Cu(OTf)2]. 

In the presence of electron-deficient dienophiles such as tetracyanoethylene (TCNE), however, vinylallene 198 acts as a diene to afford cross [4+2]-cycloadducts. In the case of 1,4-naphthoquinone, the adduct 199 was converted to 1-methylanthra-quinone 200 in the presence of charcoal [163],... 

The reactivity of stable germaphosphenes has been previously investigated and reviewed.3,4,7 The chemical behavior of Mes2Ge = PAr 155 toward orthoquinones (tetrachloro-o-benzoquinone, 3,5-di-terr-butyl-o-benzoqui-none, and 1,2-naphthoquinone) and ce-diketones (benzil and biacetyl) has been examined. The reaction with o-quinones involved probably radical intermediates, and in each case only the less encumbered isomer of the corresponding [2 + 4] cycloadduct 156 was formed. Benzil led in a very similar manner to a l,4,2,3-dioxagermaphosphin-5-ene 157, whereas, as was observed with acetone, an ene-reaction occurred with biacetyl to afford 158138 (Scheme 29). 

A -Sulfonyl-2,2 -biindoles undergo a formal [4-I-2] cycloaddition with various dienophiles to produce indolocarba-zoles <2004TL4009>. Thus, reaction of 171 with A -benzylmaleimide in chlorobenzene in a sealed tube produces the cycloadduct in moderate yield (Equation 105) as the only observable product (Table 11). It is proposed that the reaction proceeds by an initial Michael addition, followed by a rapid cyclization and loss of the phenylsulfonyl group during the aromatization process. Similar cyclization reactions are observed with A -methylmaleimide, dimethylace-tylene dicarboxylate, and 1,4-naphthoquinone. 

The intramolecular 2 + 2-photo-cycloadditions of optically active allenesilanes (5) with enones and enoates produce silyl-substituted exo-methylenecyclobutanes (6) in high enantiometric excess. Photo-desilation leads to the parent unsaturated exo-methylenecyclobutanes (7) (Scheme 3).19 The cycloaddition of naphthoquinone to allyltrimethylsilane in the presence of Me2 A1C1 yields the expected 2 + 2-cycloadduct that slowly rearranges to the 2 + 3-adduct.20 hi the presence of bases, Cephalosporin triflates (8) undergo 2 + 2- and 4 + 2-cycloaddition with alkenes, alkynes, and dienes via an intermediate six-membered cyclic allene (9) (Scheme 4).21... 

A computational study has been carried out593 on the rearrangement reactions of methylsilacyclopropane, and the pathway shown in Scheme 118 has been put forward594 to account for the formation of product (459) from the reaction of Me2AlCl with the (2 + 2)-cycloadduct (458) between naphthoquinone and allyl trimethylsilane. 

Sulfur-substituted 3-vinylpyrroles generated from A -methyl-3-thioace-tylpyrrole have been used to accomplish the synthesis of functionalized indoles by Diels-Alder cycloaddition. In the reactions with MA, NPMI, and naphthoquinone the [4 + 2]-cycloadducts were obtained with low to moderate yields and directly transformed to the corresponding indoles by treatment with DDQ (91CPB489). 

The reaction of the 2,3-ethylenic bond of 1,4-benzo- and naphthoquinones yields the cycloadducts 80 (Equation 23) <2005CC2366>. The ionization potential of 1,4-naphthoquinone (9.5 eV) is lower than that of 1,4-benzoquinone (10.11 eV), and therefore the cycloaddition reaction of 1,4-naphthoquinone proceeds faster. 

The Diels-Alder cycloaddition reaction between the transient diene 208 and /i-quinonic dienophiles such as /i-benzoquinone or 1,4-naphthoquinone, followed by further aromatization with DDQ, afforded cycloadducts 216 and 217, which were used for the preparation of TTF derivatives (Scheme 26) <1998CC2197, 2000TL2091>. 

An unusual formation of naphtho[2,3-c]pyrazole-4,9-diones 191 was observed when actinorhodin, a red pigment from Streptomyces, or other bis( 1,4-naphthoquinone) derivatives were treated with diazomethane. The reaction involved the formation of a cycloadduct (64CB2555), and thereafter... 

Isoquinoline-5,8-diones undergo Diels-Alder cycloaddition to give derivatives of the linear system similar to 283 (69JHC697). Cycloaddition between 1,4-naphthoquinone and l-dimethylamino-3-methyl-2-azabutadiene gives cycloadducts in moderate yield (75JA4409 82TL3261). 

Binaphthol catalyst 417 proved effective in the cycloadditions of l-alkoxy-l,3-butadie-nes with methacrolein and l.d-naphthoquinone . More recently, it was found that the use of molecular sieves was essential for the in situ preparation of the catalyst, but also that this had dramatic effects on the enantioselectivity . In the presence of molecular sieves, the cycloaddition of juglone (342) with l-acetoxy-1,3 butadiene was catalyzed by 10 mol% of 417 to give cycloadduct 343 with only 9% ee. In the absence of molecular sieves, the enantiomeric excess increased to 76-96% (equation 124). 

One of the early examples of an intramolecular Diels-Alder reaction of benzynes involved cycloaddition to a furan that was tethered to the benzyne moiety . Diazoti-zation of anthranilic acid 669 gave in 86% yield the cycloadduct 670, which was subsequently converted to the o-naphthoquinone 671 (mansonone E 7 steps) as well as to the structurally related mansonones F and I and biflorin. ... 

Dipolar cycloaddition of glycosyl azides 245 to 1,4-naphthoquinones has been observed. At room temperature, the l-glycosylnaphtho[2,3-J]triazole-4,9-dione (266) was formed selectively in low yield at elevated temperatures decomposition of the cycloadduct took place and several transformation products of 266 were identified. 

This group " also diverted the usual Diels-Alder cycloaddition pathway of Reissert salts with olefinic esters to a 1,3-dipolar cycloaddition pathway by the addition of triethylamine. Thus treatment of munchnone imine 364 with ethyl acrylate and triethylamine affords the 1,3-dipolar cycloaddition product 366 (30%) as the major product, formed by fragmentation of cycloadduct 365 (Fig. 4.121). The Diels-Alder product (not shown) is formed in 15% yield. Similar products to 366 are formed with dimethyl and diethyl maleate and fumarate. Laude and coworkers " also were able to trap munchnone imine 367 with dipolarophiles to furnish 368 (Fig. 4.122). No Diels-Alder cycloadducts derived from the oxazolium salt were detected. In contrast, fumarate and acrylate esters give only Diels-Alder cycloadducts from the tautomeric oxazolium salt (not shown). However, benzo-quinones and 1,4-naphthoquinone react in a 1,3-dipolar fashion with munchnone imine 372 derived from Reissert compound 369 to give 373 (Scheme 4.11). " Diels-Alder cycloadducts derived from oxazolium salt 371 were not observed. In a... 

Diels-Alder addition of (1) to alkenic dienophiles furnishes cy-clohexenone derivatives (eqs 3 and 4). Addition of (1) to naphthoquinone afforded a mixture of several cycloadducts which could be oxidized to a single anthraquinone (eq 5). 

Also, the 1,2-dichloro-1,4-naphthoquinone reacts with phenylallene under photolytic conditions to give a 74 % yield of the [2+2] cycloadduct In contrast, 1,4-benzoquinone (87 % yield) and 1,4-naphthoquinone (40 % yield) react with tetramethylallene in the presence of light to give the cyclic ketones 194. ... 

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